In the background art, vector base amplitude pannning (VBAP) is known as a technique of controlling the localization of a sound image using a plurality of loudspeakers (see, for example, Non-Patent Literature 1).
In VBAP, a target position where a sound image is to be localized is represented by a linear combination of vectors pointing to two or three loudspeakers placed around the target position. Also, gain adjustment is performed so that a sound image is to be localized at the target position, where coefficients multiplied by the respective vectors in the linear combination are used as the gains of sound signals output from the respective loudspeakers.